1. Field of the Invention
The present invention relates to a process for the preparation of 1-{[5-(4-hydroxy-2H-1,2-benzothiazin-3-yl)-1,2,4-oxadiazol-3-yl]methyl}eth anone S,S-dioxide (III).
2. Description of the Prior Art
Lombardino, in U.S. Pat. No. 3,853,862 has disclosed the preparation of a series of 4-hydroxy-1,2-benzothiazine carboxamides by metal hydride ring closure of N-alkylated benzenesulfonylglycineamides. N-(5-methyl-3-isoxazolyl)-N'-methyl-N' -(2'-methoxycarbonylbenzenesulfonyl)glycineamide is among the glycineamides which may be ring closed according to the Lombardino process.
Zinnes et al. describe ring closure of the corresponding ketone (N-acetonyl-o-carbethoxybenzenesulfonamide) to form the 3-acetonylbenzothiazine, using sodium ethoxide, J. Org. Chem. 30: 2241-2246 (1965).
Rearrangement reactions of substituted isoxazoles and oxadiazoles are discussed generally in H. C. Van Der Plas, Ring Transformations of Heterocycles, Volume 1, Chapter 3, 1973, Academic Press, London, New York.